1. Field of the Invention
The invention relates to evaluation and/or design of flooding processes for enhanced oil recovery.
2. Brief Description of the Prior Art
A great need exists to recover additional hydrocarbons from subterranean formations after primary production is no longer economical. Recovery processes involving mobilizing and moving hydrocarbons through a hydrocarbon-bearing subterranean formation from an injection well to a production well by injecting a mobilizing fluid into the injection well are well known. For example, water flooding is widely practiced all over the world. A large amount of funds and effort are now also being expended in developing and demonstrating surfactant floods, polymer floods, steam floods, micellar floods, CO.sub.2 floods, and the like.
One of the factors inhibiting more rapid development of such enhanced recovery methods, particularly surfactant flooding, polymer flooding, micellar flooding, and the like, is the tailoring of a process to a reservoir. Hydrocarbon-bearing reservoirs are each unique and can respond in many unexpected and unpredictable ways to application of such complex processes. Particularly, applications of surfactant systems are unpredictable because so many parameters can influence the surfactant systems.
Present practice is to use all of the knowledge available including laboratory data and reservoir properties to design a best evalution of what will be technically feasible and cost effective in the reservoir, and then to conduct a pilot project for each reservoir to prove out or redesign the flood process.
A major problem with this approach is that pilot projects are quite expensive and take an extended time. For example, a pilot project to evaluate a surfactant or polymer flood can be expected to cost at least $3 million. To illustrate, BERC-76/4, October 1976 Progress Review No. 8, Contracts and Grants for cooperative research on Enhancement of Recovery of Oil and Gas, and other current references, disclose that the ERDA supported project in the El Dorado field had an original estimated cost of over $7 million, the project in the Burbank field had an estimated cost of almost $10 million, the Bell Creek field over $5 million, the Bradford field over $4 million, and the North Stanley field almost $4 million. Many larger companies are also independently conducting pilots having costs of this order of magnitude. Obviously, only the expectation of considerable hydrocarbon recovery can justify such front-end risk expense. The time involved for such evaluation normally extends over a number of years. Thus only the larger reservoirs are evaluated, and only organizations with considerable risk capital can afford to evaluate such processes.
Clearly, a great need exists for a less expensive and a more rapid method of field evaluating and tailoring such flooding processes in particular reservoirs. The single well tracer method employed in the process of this invention is disclosed in U.S. 3,623,842. This patent forms the basis of a license package of a method for determining hydrocarbon saturation in subterranean reservoirs, and along with related know-how and softwear has been widely licensed in the industry by Exxon Co., Houston, Texas. This patent is incorporated by reference. Supplemental disclosure is found in: U.S. Pat. No. 3,590,923; Clyde Q. Sheely, Description of Field Tests to Determine Residual Oil Saturation by Single Well Tracer Method, SPE paper 5840, Prepared for the Improved Oil Recovery Symposium of the Society of Petroleum Engineers of AIME, held in Tulsa, Okla., March 22-24, 1976; J. F. Tomick, et. al., Single-Well Tracer Method to Measure Residual Oil Saturation, Journal of Petroleum Technology, February, 1973, pp. 211-218. Such disclosures are also incorporated by reference.
Our invention constitutes a substantial advance in the art by providing for efficient acquisition of data useful to evaluate the effectiveness of or to design an enhanced recovery process. Cost is greatly reduced since only one bore hole need be drilled, and the time is also greatly reduced.